Morphology and phase control of fluorides nanocrystals activated by lanthanides with two-model luminescence properties.

The morphology, size and phase control of luminescent fluoride nanocrystals through doping has become a new research hotspot due to their improved properties. In this work, Yb(3+) ions, as one of the most efficient sensitizers for various lanthanide activators, were doped in NaGd(Y)F(4) nanocrystals. The results show that no obvious influence was observed for Yb(3+)-doped NaYF(4) nanocrystals, while the influence of Yb(3+) doping on NaGdF(4) nanocrystals was remarkable. The NaGd(1-x)Yb(x)F(4) nanocrystals were synthesized by a hydrothermal route and had a morphology of rice-like nanorods. By controlling the synthesis parameters, the average size and slenderness of the nanocrystals increased gradually with addition of Yb(3+) ions. In contrast, the NaGd(1-x)Yb(x)F(4) nanocrystals maintained a hexagonal phase, which is more beneficial for application as a luminescent host, until the content of Yb(3+) ions reached x = 0.9. The growth and transformation mechanism of NaGd(1-x)Yb(x)F(4) nanocrystals was proposed to be a result of the competition between ion diffusion and an Oswald ripening process. Photoluminescence (PL) spectra confirm the efficient up-conversion and near-infrared (NIR) two-model luminescence properties of Er(3+) (Tm(3+)) activated NaGd(Y)(1-x)Yb(x)F(4) nanocrystals. Simulated analysis results indicate that a colloidal solution of mixed luminescent nanocrystals is expected to find application as the activated medium of three dimensional displays and a broadband optical amplifier.